Ceramic ballistic plates having a unitary (i.e. a single piece) configuration are known. Such unitary ceramic ballistic plates are comprised entirely of the same ceramic material composition, and thus exhibit the same bulk mechanical properties throughout the body thereof.
In a typical application, unitary (i.e. single piece) ceramic ballistic plates backed by a polymer fiber and resin composite are inserted into respective pockets located, for example, in the front and the back of a flack jacket to provide protection for the body's most vital organs from high power and high speed projectiles such as armor-piercing rounds. Other than a human body, ceramic ballistic plates can be used to protect other bodies, for example, a vehicle, aircraft, or building structure.
It is known that the ballistic stopping power of a unitary ceramic ballistic plate can be severely degraded after being stricken by a projectile, not only at the point of impact, but also at locations relatively farther away from the point of impact because of cracks that propagate and extend away from the point of impact through the body of the unitary ceramic ballistic plate. The reason for the possibility of the body-wide crack propagation is that the plate is made entirely of the same brittle material composition with the same bulk mechanical properties throughout the body thereof; including properties that relate to the response of the material to crack propagation.
Efforts are currently being undertaken to develop a standard ESAPI (enhanced small arms protective insert) plate with multiple segments (each segment being a discreet unitary body of a ceramic ballistic material) fitted together to make up the overall shape of a standard single unitary ceramic ballistic plate. By using multiple segments, the advancement of cracks created by the impact of a projectile can be restricted to the boundary of the segment receiving the impact in that an advancing crack cannot travel beyond the edge of a segment to another segment within the multi-segment ceramic ballistic body. As a result, compared to a unitary ceramic ballistic plate that is made entirely of the same ceramic material, a multi-segment ceramic ballistic plate, that has been stricken by a projectile, is expected to exhibit a lesser degradation of its overall ability to resist damage by subsequent projectiles.
A drawback to a multi-segment ceramic ballistic plate, however, is the presence of seams between the segments. Seams, which are physical discontinuities in a multi-segment ceramic ballistic plate, render severe inconsistency in the ballistic stopping power of a multi-segment plate in that the seams have little to no ballistic stopping capability.
Thus, it is desirable to have a unitary, seamless, and physically continuous ceramic ballistic plate that does not exhibit the disadvantages of the unitary ceramic ballistic plates of the prior art and/or the disadvantages of a multi-segment ceramic ballistic plate.
An armor plate according to the present invention is a monolithic, unitary, seamless and physically continuous ceramic body having first regions of one mechanical property, one chemical composition, and one microstructural composition isolated from one another by a network of second regions of another mechanical property different from the one mechanical property; another chemical composition, and another microstructural composition, the one mechanical property and the another mechanical property being the propensity to propagate or arrest a crack.
In one embodiment, the first regions have a lesser propensity to branch cracks than the second regions, while in another embodiment the first regions have a higher propensity to branch cracks than the second regions.
An armor plate according to the present invention may be comprised of a base ceramic material such as boron carbide or silicon carbide in which the first and second regions have different chemical compositions and/or microstructural make up (composition). For example, the base ceramic may be silicon carbide, the first regions may have low to no graphite content while the second regions may have a higher graphite content, e.g. more than 2.5% by weight and up to 25% by weight of graphite. Alternatively, the base ceramic may be silicon carbide with no or little secondary phases in the first regions thereof, while the second regions include grain boundary phases containing yttrium and aluminum oxides to weaken the second regions. When the base ceramic is boron carbide, the first regions may include little to no graphite, while the second regions may include a larger amount of graphite in order to enhance its propensity to branch and capture cracks.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.